<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 600px;
            margin: 100px auto;
        }
        .message{
            display: inline-block;
            font-size: 12px;
            color: #999;
            background: url() no-repeat left center;
            padding-left: 20px;
            
            
        }
        .wrong{
            color: red;
            background-image: url(images/wrong.png);

        }
        .right{
            color: green;
            background-image: url(images/right.png);
        }

    </style>
</head>
<body>
    <div>
        <div class="register">
            <input type="password" class="ipt">
            <p class="message">请输入6~16位密码</p>
        </div>
        <script>
            var ipt = document.querySelector('#ipt');
            var message = document.querySelector('.message');
            // 添加事件  失去焦点
            ipt.onblur=function(){
                //根据表单的长度判断
                if(this.value.length < 6 || this.value.length >16){
                    message.className='message wrong';
                    message.innerHTML='您输入的位数不对 要求6-16位'
                }else{
                    message.className='message right';
                    message.innerHTML='您输入的正确';
                    
                }
            }
        </script>
</body>
</html>